The Kjeldahl method was introduced in 1883 and consists of three main steps: sample digestion, distillation, and ammonia determination (titration being the primary method). The Kjeldahl method uses sulfuric acid, a variety of catalysts, and salts to convert organically bound nitrogen in samples to ammonium with its subsequent measurement (Saez-Plaza et al., 2013). Today, this method is universally accepted and used in tens of thousands of laboratories throughout the world for nitrogen analysis in a wide variety of materials, such as foods, beverages, agricultural products, environmental samples, chemicals, biochemicals, and pharmaceuticals. However, successful analysis requires proper sampling and sample handling, which depend on the type of material. The Kjeldahl method has been validated and standardized for total (crude) protein estimation for a wide variety of food matrices, indirectly determined by their nitrogen content, and is the reference method adopted by many international organizations. The Kj...

An Overview of the Kjeldahl Method of Nitrogen Determination. Part II. Sample Preparation, Working Scale, Instrumental Finish, and Quality Control

In 1883 Kjeldahl devised a method for the determination of nitrogen, which has become a classical measurement in analytical chemistry and has been used extensively over the past 130 years. In the original method, sulfuric acid alone was used as a digestion medium. The use of a catalyst in Kjeldahl digestion accelerates oxidation and completes the digestion to allow the subsequent determination of nitrogen. Mercury (its use being in decline because of environmental concerns), selenium, and copper are the catalysts of choice, though for certain applications titanium has found some usage. Short digestion times in association with maximum nitrogen recovery may be achieved by using a methodology based on experimental design and response surfaces, with microwave digestion processes, and with the aid of the couple sulfuric acid-hydrogen peroxide without catalyst. The quantification of distilled ammonia is generally achieved by titration; the ammonia is absorbed in an excess of boric acid, followed by titration w...

An Overview of the Kjeldahl Method of Nitrogen Determination. Part I. Early History, Chemistry of the Procedure, and Titrimetric Finish

A white calcium bentonite (CaB) from the Kutahya region, Turkey, contains 35 wt. % opal-CT and 65 wt. % Ca-rich montmorillonite (CaM). Samples were heated at various temperatures between 100–1300°C for 2 h. Thermal gravimetric (TG), derivative thermal gravimetric (DTG), and differential thermal analysis (DTA) curves were determined. Adsorption and desorption of N2 at liquid N2 temperature for each heat-treated sample was determined. X-ray diffraction (XRD) and cation-exchange capacity (CEC) data were obtained. The change in the d (001) value and the deformation of the crystal structure of CaM depend on temperature. Deformation is defined here as changes of the clay by dehydration, dehydroxylation, recrystallization, shrinkage, fracture, etc. The activation energies related to the dehydration and dehydroxylation of CaB calculated from the thermogravimetric data are 33 and 59 kJ mol−1, respectively. The average deformation enthalpies, in the respective temperature intervals between 200–700°C and 700–900°C, were estimated to be 25 and 205 kJ mol−1 using CEC data and an approach developed in this study. The specific surface area (S) and the specific micropore-mesopore volume (V) calculated from the adsorption and desorption data, respectively, show a “zig zag” variation with increasing temperature to 700°C, but decrease rapidly above this temperature. The S and V values were 43 m2 g−1 and 0.107 cm3 g−1, respectively, for untreated bentonite. They reach a maximum at 500°C and are 89 m2 g−1 and 0.149 cm3 g−1, respectively. The XRD data clearly show that, at 500°C, where the irreversible dehydration is completed without any change in the crystal structure, the porosity of CaM reaches its maximum.

The effect of thermal treatment on some of the physicochemical properties of a bentonite

Publisher Summary This chapter presents three methods for determination of total nitrogen, such as microvolumetric method, submicrospectrophotometric method, and ultromicromethod. Total nitrogen in biological materials and in enzymatic reaction mixtures is determined by three steps which involve digestion, oxidation, and distillation.There is not yet a universal digestion procedure for the determination of all types of organic and inorganic nitrogen compounds. Therefore, this chapter presents various methods for digestion of mixtures. First method described for digestion includes Kjeldahl flask and H 3 PO 4 , H 2 SO 4 , and potassium persulfate. Second method is Kjeldahl-Gunning-Dye modification, which involve sucrose, mercuric oxide, potassium sulfate, and concentrated sulfuric. When inorganic nitrogen is present as nitrates or nitrites, the Kjeldahl-Gunning-Jodlbauer process is satisfactory. The steam distillation of ammonia from an alkalized digest is the most rapid and quantitative method for the recovery of the ammonia. Numerous methods for the titration of the ammonia after its separation have been used, several of which are presented in the methods chapter based on iodometric method.

H. K. Alber

Papers

Recommended Specifications for Microchemical Apparatus. Micro-Kjeldahl Nitrogen

Report on Recommended Specifications for Microchemical Apparatus

Report on Recommended Specifications for Microchemical Apparatus

Recommended Specifications for Microchemical Apparatus-Carius Method

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